Can you explain to me what the last sentence mean in the following passage please ? Especially I could not figure out the meaning of the parts of " to amount to much that " and " others had of them"
In the 1970s, sociologist William Chambliss studied two groups of high school boys to find out how strongly labels affected them. The eight boys in the group Chambliss called the Saints came from middle-class families. Society expected them to do well in life. The six boys in the other group, the Roughnecks, came from lower-class families in poorer neighborhoods. The community generally expected them to fail. Both groups engaged in deviant behavior—skipping school, fighting, and vandalizing property—but suffered different consequences. The teachers, the police, and the community excused the Saints’ behavior because they believed the Saints were good boys overall. The same people saw the Roughnecks as bad and prosecuted them for their behavior more often.
Years later, all but one of the Saints had gone to college and subsequently into professional careers. Two Roughnecks went to college on athletic scholarships, graduated, and became coaches. Two never graduated from high school, and the other two ended up in prison.
Chambliss discovered that the boys’ social class had much to do with the public’s perception of them and the ways the public perceived their acts of deviance. He also hypothesized that a deviant label can become a self-fulfilling prophecy. The Roughnecks had heard for so long that they were never going to amount to much that they behaved in accordance with the negative expectations others had of them.